- Maintenance: Beginning 2-3 weeks after reinduction, all patients receive oral mercaptopurine daily and oral methotrexate weekly for 2 years. Except for LR-R and HR-R, patients also receive pegaspargase IV over 2 hours every 3 weeks for 3 doses. Patients who have not undergone CNS radiotherapy receive methotrexate IT at 3, 6, and 9 months.